The present invention relates to airbags for use in vehicles as a passive passenger restraint in the event of an accident, and more particularly for seamless woven bags suitable for use therein and methods of making the same.
An airbag is typically made with a bag which is formed by sewing or stitching together a pair of separate and distinct panels or by folding over an oversize piece of material and stitching the free edges thereof together. In either case, the cost of manufacturing the bag far exceeds the cost of weaving the bag due to the need for the seaming operation (i.e., stitching or sewing) and the additional time required to perform that operation. Equally important, while the weaving of the bag is a reliable and dependable operation requiring only minimal quality control, the seaming operation is greatly less predictable and reliable and indeed necessitates extensive and careful inspection procedures to ensure that the finished bag meets its specifications. These inspection procedures further increase the final cost of the bag.
Seamless bags of integral, unitary, one-piece woven construction are known. For example, U.S. Pat. Nos. 592,057; 3,340,919; 3,360,014; and 3,544,404 describe bags which are useful for containing granular solid material such as sand, coffee, food grains and the like. Each of these patents discloses designs which relate to the ability of the bag to hold a great quantity of weight (e.g., sand), the need to open and fill the bag (e.g., by opening the bag at one of the edges thereof), and the problems that result from stressing of the woven material where the two panels join together (variously referred to as the uniting band, the single ply cutting strip, the double thickness single layer fabric portion, or the single thickness strip).
Such prior art seamless bags are not suitable for use in airbags, however, and the design considerations applicable to airbags differ from those applicable to sand bags and the like. For example, typically an airbag must have a low Frazier porosity (e.g., less than eight cubic feet per minute (CFM) for a Passenger side airbag and less than 2 CFM for a driver side airbag) and must be capable of being rapidly inflated with nitrogen or other gas (e.g., within one hundred milliseconds) and then deflating. To this end, a uniform distribution of permeability is crucial. Therefore, the uniting band must not suffer combing or windowing--i.e., the formation of gaps in the yarn under stress as a result of compaction--as such gaps would permit gases to flow therethrough. A non-uniform permeability about the interface between the separate panel areas, on the one hand, and the uniting band thereabout, on the other hand, such as might result from combing or windowing, would present a problem because hot gases (about 1000.degree. F.) could concentrate at stress points exhibiting gaps or small holes and cause melting failures. Accordingly, a bag suitable for use in an airbag should not allow substantial compression of gases to occur in that interface area.
Additionally, an airbag does not have an opening at one of the edges, but rather a hole cut into the center of one of the opposed panels for subsequent attachment of an inflating device.
Accordingly, it is an object of the present invention to provide a seamless bag of integral, unitary, one-piece woven construction suitable for use in an airbag.
Another object is to provide an airbag using such a seamless bag.
A further object is to provide a method of making such a seamless bag.